NEW-WAVE CROPS HEADING FOR THE FARM. Corn that fights off pests, tomatoes that resist disease, potatoes with a higher food value - these are just a few of the biotech products springing from test tubes today. If field tests show that these plants don't pose ecological risks, agrigenetics could have a big impact on the farm by the turn of the century.

IN the Netherlands, Mogen International scientists are ready to field-test potatoes that carry a foreign gene to combat viral infection. In Australia, genetic engineers of the Commonwealth Scientific and Industrial Research Organization are preparing to try out their protein-rich alfalfa designed to boost wool growth when fed to sheep. And in the United States, Crop Genetics International received final Environmental Protection Agency approval last month to field test corn that will carry within its vascular system a patented strain of bacterium genetically altered to kill the European corn borer.

As genetic engineers focus their skills to help the farmer, all over the world they are moving their experiments out of the laboratory and into the field. Experimenters in five countries, including the US, have already conducted about two dozen field tests of genetically engineered organisms, according to the US Congressional Office of Technology Assessment (OTA) in its lat- est biotechnology report, released May 4. Many others are in the offing. These small-scale field tests, to be carried out over the next few years, will be so carefully controlled that they ``are unlikely to result in environmental problems,'' says an OTA statement. It adds, ``If small-scale field tests do not identify areas of significant concern, there would be no scientific reasons not to proceed with field tests or applications on a larger scale.''

Thus, genetic engineering - direct manipulation of the genetic makeup of agriculturally important organisms, as opposed to standard breeding - is developing rapidly. It is likely to start having a significant effect on farming by this century's end, a mere dozen years from now.

OTA reflects a virtual global consensus among experts when it says that this technology prom- ises many benefits. It can boost the food value of crops. It can improve livestock. It promises to reduce our dependency on environmentally damaging chemicals by giving crops an ability to protect themselves against pests.

OTA also reflects a widely held concern when it notes that the deliberate release of these genetically engineered organisms sets an ecological precedent that has risks. The report explains:

``Virtually any organism deliberately introduced into a new environment has a small but real chance of surviving and multiplying. In some small subset of cases, an undesirable consequence might follow. The complexity of even simple ecosystems makes the precise prediction of such events, and of the consequences, difficult. ... Although there is some consensus in the scientific community that the likelihood of unique or serious problems from planned introductions is quite low, this opinion is not held unanimously.''

Thus, hand in hand with the application of genetic engineering to farming, scientists involved recognize that they must design those applications with the possible ecological consequences strongly in mind. This will be considered in more detail in the third installment of this three-part series.

One of the main factors promoting the move from laboratory to field tests has been the breakthrough in this decade in applying genetic engineering to plants. Scientists designing novel microbes for farm use have had the benefit of genetic-engineering tools developed for use with bacteria and viruses during the '70s. Their field tests were slowed in the early 1980s more by concern over safety and proper regulation than for technical reasons.

Genetic engineering of animals is in such an early stage that the need for widespread tests has not yet arisen. But some designer plants and plant-bacteria combinations are ready for takeoff.

The first big advance came with the use of a plant pest - a bacterium called Agrobacterium tumefaciens - that causes crown gall. These bacteria contain a small gene-carrying body called the Ti (tumor inducing) plasmid that easily carries new genes into plant cells. Geneticists disarmed the Ti plasmid's gall-inducing ability and learned to use the plasmid to carry the genes they wanted into plant cells. These might be useful genes from other plant species or bacteria, or genes that genetic engineers synthesize. So far, cells of at least 15 plant species have been transformed this way and have been regenerated to produce whole fertile plants. But the technique, at least at first, was limited to the dicots - flowering plants with two seed leaves such as tomatoes and potatoes. It didn't work with the monocots - flowering plants with one seed leaf, such as grasses. That, for a time, left the world's great cereals beyond the genetic engineer's grasp.

Over the past five years, however, the genetic designers have learned to work with monocots, too. Some have learned to use the Ti plasmid with certain monocots, as when Willi Sch"afer, Andrea G"orz, and G"unter Kahl of the University of Frankfurt, West Germany, last year reported transforming a yam this way. Other scientists remove plant cell membranes and allow the cells to take up genetic material before reconstituting them.

Some experimenters are trying exotic techniques. Theodore M. Klein, Edward D. Wolf, Ray Wu, and John C. Sanford of Cornell University made headlines last year when they showed how to use a shotgun literally to shoot microscopic gene-carrying pellets into plant cells.

Not to be outdone by old-fashioned weaponry, Michael Berns and associates at the University of California, Irvine, campus are using a microscope-directed laser to punch a small hole in cells. Before the hole closes, new genetic material flows into the cell.

Whatever their techniques, genetic engineers are now working with many of the major food plants. They are trying to improve their food value and resistance to pests (see accompanying story). They are even exploring genetic changes that confer drought resistance or help plants tolerate brackish water.

Robert Beachy of Washington University at St. Louis is typical of these agricultural pioneers. He has been working with scientists of the Monsanto Company to make tomatoes resistant to the tobacco mosaic virus. His discovery enables the plant to make a protein ``overcoat'' that sheathes the virus. Since the transformed plant cells now make this protein themselves, it acts as a shield against the virus. The technique has also worked for alfalfa, cucumbers, and potatoes.

In fact, Professor Beachy says, ``We believe the genetic engineering approach we have used will be applicable to many different viruses and plants.'' That includes ``other vegetables, rice, and cereal grains.''

Beachy shares the general opinion of experts in this field that genetic engineering is essentially just a better way of doing what breeders have done for millennia in trying to improve agriculture. ``Genetic engineering,'' he says, ``is simply plant breeding with exquisite precision.''